Connecting: type ssh and the hostname. Disconnecting: type exit or ctrl-d or whatever on the remote end. That's enough for many people.
For a group of people as large as HN, there are bound to be many people who are experts in one thing, and marginal with others, so articles like this are likely to appeal to them, and be useful.
I would agree if it were for some more obscure yet useful feature, but this is one of the basics, that's clearly documented. This should not be useful for anyone who's ever read the man page, and anyone who's used ssh should have read the man page at least once. That so many people apparently haven't, in what's supposed to be highly technical community, is a very disappointing sign of intellectual indolence.
At more than 6 million words, that's approximately 10 War and Peace's. And of course in terms of documentation, that's only man pages, which doesn't cover all the stuff that's in other formats like info or html.
You cannot be an expert in everything: I knew about that command for closing ssh, but frankly it is not something I use because it's easier to just close the rxvt and be done with it. I have zillions of other things to occupy my brain.
I'd also argue that in terms of ssh, since this function is so easily accomplished in other ways, this is really just handy triva. Much more useful to know about are all the tunneling things, as they are not necessarily obvious, and can be extremely useful.
I'm hardly advocating reading every single man page; just the man pages for things you actually use. And 10x War and Peace's is hardly an extreme amount of reading to become a knowledgeable systems administrator. That would probably be akin to two semesters of 5 courses each to become a systems administrator; I think most community college or vocational school programs for systems administration require 2 years, and wouldn't teach you nearly as much.
In any event, I'm not taking the position that casual *nix users should be reading every single man page. Just for the essentials like ssh, cp/mv, ls, man itself, etc. You do not need to be an expert to read a few man pages on utilities you often use. Everyone should RTFM, at least for the relevant bits, no matter what level you're at. Anyone who found the initial post useful would also find reading the man page for ssh useful. Thus, they should have read it. That's not at all suggesting that they need to become an expert.
The ~. key sequence is used in pretty much any console type application, not just ssh, so it's quite useful to know. If you do any work with a serial console i.e. configuring network devices, pdus, even some servers, etc., then it's pretty useful for ending a session as there's no TCP connection to close and take you back to the local console on your terminal emulator. If you're working on the actual local console and not in a full blown GUI on a system without virtual consoles, there may be no other way to close the serial console session on some platforms (notably man different OS'es running on Sparc64's as well as not on Solaris at all until recently).
Regardless, it's generally less effort to type ~. than to close and reopen a window/tab in your terminal emulator of choice. The time spent to read the man page would inevitably be made up by a few clicks saved here and there throughout a long career. It would have taken less time than to make multiple posts in this thread.
For a group of people as large as HN, there are bound to be many people who are experts in one thing, and marginal with others, so articles like this are likely to appeal to them, and be useful.